Determine if char is a num or letter
CCharAlphanumericC Problem Overview
How do I determine if a char in C such as a or 9 is a number or a letter?
Is it better to use:
int a = Asc(theChar);
or this?
int a = (int)theChar
C Solutions
Solution 1 - C
You'll want to use the isalpha() and isdigit() standard functions in <ctype.h>.
char c = 'a'; // or whatever
if (isalpha(c)) {
puts("it's a letter");
} else if (isdigit(c)) {
puts("it's a digit");
} else {
puts("something else?");
}
Solution 2 - C
chars are just integers, so you can actually do a straight comparison of your character against literals:
if( c >= '0' && c <= '9' ){
This applies to all characters. See your ascii table.
ctype.h also provides functions to do this for you.
Solution 3 - C
<ctype.h> includes a range of functions for determining if a char represents a letter or a number, such as isalpha, isdigit and isalnum.
The reason why int a = (int)theChar won't do what you want is because a will simply hold the integer value that represents a specific character. For example the ASCII number for '9' is 57, and for 'a' it's 97.
Also for ASCII:
- Numeric -
if (theChar >= '0' && theChar <= '9') - Alphabetic -
if (theChar >= 'A' && theChar <= 'Z' || theChar >= 'a' && theChar <= 'z')
Take a look at an ASCII table to see for yourself.
Solution 4 - C
Neither of these does anything useful. Use isalpha() or isdigit() from the standard library. They're in <ctype.h>.
Solution 5 - C
If (theChar >= '0' && theChar <='9') it's a digit. You get the idea.
Solution 6 - C
You can normally check for ASCII letters or numbers using simple conditions
if ((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z'))
{
/*This is an alphabet*/
}
For digits you can use
if (ch >= '0' && ch <= '9')
{
/*It is a digit*/
}
But since characters in C are internally treated as ASCII values you can also use ASCII values to check the same.
Solution 7 - C
C99 standard on c >= '0' && c <= '9'
c >= '0' && c <= '9' (mentioned in another answer) works because C99 N1256 standard draft 5.2.1 "Character sets" says:
> In both the source and execution basic character sets, the value of each character after 0 in the above list of decimal digits shall be one greater than the value of the previous.
ASCII is not guaranteed however.